1. Field of the Invention
The present invention relates to a one-step process for bonding a manifold to a printhead and interconnection board located on a heat sinking substrate. The one-step process provides encapsulation of wire bonds, sealing of any air gap between the manifold and the printhead along a front face, and enhances structural bonding of the manifold to printhead components.
2. Description of Related Art
The thermal ink jet printhead is a device which ejects fluid (ink) in a controllable fashion by means of electrical pulses passed through resistive heating elements which are in thermal contact with the ink. Ink from a reservoir travels through a manifold located above the printhead and into the printhead through an ink inlet. A printhead die consists of a channel plate (in which fluidic pathways are formed for example by etching) bonded on top of a heater plate (containing heating elements, leads and preferably some addressing electrodes to reduce required interconnection density). Insofar as possible, the microelectric packaging of the printhead die follows IC and hybrid industry standard methods such as epoxy die bonding of the silicon device onto the substrate, as well as wire bonding to accomplish electrical interconnection. However, the fluidic handling requirements of the printhead give rise to additional packaging requirements.
A water tight seal needs to be formed between the manifold and the die to contain the ink in the proper channels for delivery without leakage from the manifold. However, this watertight seal is not strong enough or extensive enough to provide a good structural bond between the manifold, the printhead die and other printhead components.
In addition, when the manifold is placed over the die, there is a small air gap between the ends of the die and the legs of the manifold. The air gap, if not filled, allows a passageway for humid air to escape when the printhead is capped, so that the cap does not effectively prevent evaporation of volatile ink components.
Additionally, wire bonds connecting the die to an interconnection board need to be encapsulated to provide protection against mechanical damage and corrosion.
Prior printhead manufacturing techniques address some of these problems individually, such as U.S. Pat. No. 4,612,554 to Poleshuk which bonds a printhead to a daughterboard and wire bonds electrodes of the printhead with corresponding electrodes of the daughterboard. The wire bonds are then encased in an insulative epoxy. The disclosure of U.S. Pat. No. 4,612,554 is herein incorporated by reference.
However, prior printhead manufacturing techniques implement several individual processes to provide a printhead which is wire bonded to an interconnection board and to seal any air gap. Additionally, these prior printheads are deficient in structural bond integrity between the manifold and various printhead components. All of these previous manufacturing techniques involve excess processing time and expense or are deficient in structural integrity or air gap filling.
There is a need for a process which can address all of these problems and provide good structural bonding in a single step to reduce printhead manufacturing costs and provide an enhanced structural bond between the manifold and other printhead components.